For a long time it was common to translate the name of royals and nobles, both first names and titles, into the prefered language. In The Netherlands for example Grand Duke Jean of Luxembourg went by the first name of “Jan”, his son Henri was often called “Hendrik”. Although it has become less usual, it is still not uncommon, and in Spain magazines still often use the Spanish versions of names. For example the King of the Netherlands, Willem-Alexander is in Spanish “Guillermo Alejandro”. When it comes to first names I prefer to use what royals and nobles themselves use (d). It is a bit more difficult with titles. If I’d write “von Bayern” lots of visitors likely wouldn’t know I mean “of Bavaria”, and if I’d write “von Preussen”, which means “of Prussia”, many wouldn’t understand me either I guess at least. Luckily the difference between the German and English versions of Württemberg (sometimes in English still Wurtemberg), Hannover (Hanover) and Hessen (Hesse) isn’t that big.
Even genealogical publications are not always reliable when it comes to spelling of names. It still happens that I find in newspapers or internet sources that people themselves use(d) different spellings of their names, or even a different order or partly different names. Or the books give the wrong call name. Georg Graf Henckel von Donnersmarck died on 2 August in Austria. It took me a while to find him in the Genealogisches Handbuch des Adels as it turned out that he was listed there as Georg ALEXANDER, Alexander being the call name. The death announcement however only gives the name of Georg. I am certain Alexander is his second first name, but not the one he used in daily life as is stated in the book … And there are much more examples.